Horizontal forces of a wheel that is rolling and slipping while subjected to a coupled moment?

I am trying to understand what's going on with this problem: I summed the forces in the $x$ -axis, which is horizontal, and I thought the moment would create a force opposing the friction force. However, the given solution only included the friction force: $F_\text{friction} = ma.$ My equation was: $F_\text{friction} - M/r = ma.$ Why is the force caused by the moment excluded? Is it because there is slipping? If that was the case, would you include the force caused by a moment in a non-slipping scenario?